Yes - identify their industry (and also important "related industries") and show how the internet can increase their product and brand awareness and sales.
Locate instances in their industry where competitors are using eCommerce and websites to increase their market reach.
Search Engines: use Overture Keyword search stats and other stats fom search engines that provide them
Directory Statistics are good - like stat sheets from the bigger players like YP CS etc... - how many times does X category get visited / month etc...
I just put these stats up on one of our sites - shows typical popularity of industry and business
<snip> no links to your own sites, please</snip>
[edited by: Travoli at 5:06 pm (utc) on Mar. 3, 2004]